The present invention relates generally to semiconductor manufacturing and more specifically to a method for accurate measurement and recordation of boron and phosphorus caused impurities in semiconductor insulator layers.
Silicon compounds, such as silicon dioxide (SiO2), that can be used as insulators are particularly valuable on electronic substrates. Such insulators serve as protective coatings, inter-layer dielectric layers, doped dielectric layers to produce transistor-like devices, multilayer devices, etc.
Unfortunately, development of high integration and high-density very large-scale integrated circuits has progressed so rapidly that earlier silicon (Si) compounds have become less than satisfactory. To meet the recent needs of miniaturization of high-density semiconductor devices, a technique of forming a flat insulating layer under low temperature conditions, which utilizes flow on silicate glass, has started to come into use.
Silicate glass is easily flattened and makes a good insulating layer. Thus, silicate glasses such as borophosphotetraethylorthosilicate (BPTEOS) and borophosphosilicate (BPSG) glass have come into use.
Typically, the silicate glass is deposited in a spin-on deposition process in a liquid form in a nitrogen atmosphere. The silicate glass is then subjected to thermal treatment to allow for proper planarization and stress relief. Without the thermal treatment, incorrect concentrations of the boron (B) and phosphorus (P) elements will result in a non-planar surface and stresses, which can lead to de-lamination, and flaking of subsequently deposited layers.
One problem with boron and phosphorous is that they are hydrophilic (attract water) elements and they start to form precipitates immediately after deposition of the silicate glass. These precipitates may cause short-circuiting of the electrical interconnections, which are later formed on the silicate glass.
This has not been a major problem during semiconductor fabrication because the processing, which includes the formation of contacts, interconnects, and vias are performed in a nitrogen atmosphere.
However, during pilot or calibration runs, pilot (dummy) or calibration wafers are run through an insulator deposition machine and then are measured in air under an infrared radiation instrument to obtain the concentrations of both boron and phosphorus prior to going into production operation. Such measurement instruments as the BIO-RAD instrument from Bio-Rad Laboratories, Inc. at 237 Putham Ave. in Cambridge, Mass., are used.
Also, pilot wafers are run after the deposition machine undergoes any type of maintenance. Further, these pilot wafers may be kept for substantial periods of time in order to maintain traceability records of the production runs, which used the pilot wafers, in the event of any problems further down in the production line or out in the field.
It has been found that the insulator on pilot wafers absorbs moisture from the air as an unpredictable function of time and humidity. The absorption of moisture results in false measurements and leads to incorrect determination of the boron and phosphorus concentrations depending on how long after production the pilot wafer is measured.
It has also been noted that the calibration wafers used for the infrared radiation instruments also absorb moisture which means that the calibration standards are sometimes inaccurate and adversely affect subsequent measurements.
In the past, when these problems arose, the wafers were sent to an external laboratory for validation where the precise amount of moisture and concentration of the hydrophilic elements could be analyzed.
Unfortunately, such procedures could not give real-time measurements and were time consuming. Further, sometimes the precipitates were in the original silicate glass deposition rendering the readings inaccurate because a determination could not be made of when the precipitates were formed and thus, the true source of the precipitates. Without knowing the true source of the precipitates, the actual boron and phosphorus concentrations of the silicate glass deposited could not be determined.
As the density of semiconductor devices increases, the problem caused by impurities at lower and lower levels becomes quite substantial and a need to solve the problems related to the element caused impurities become more pressing.
The present invention a pilot or calibration semiconductor wafer having a silicate glass insulator containing a hydrophilic element for measurement or recordation purposes. The semiconductor wafer has a moisture barrier, test transparent material on the silicate glass insulator and can be placed in a moisture containing atmosphere without affecting the concentration of the hydrophilic element. The semiconductor wafer can be stored and measurements taken later to accurately determine the concentration of the hydrophilic element in the silicate glass insulator.
The present invention further provides a method for processing a pilot or calibration semiconductor wafer having a silicate glass insulator containing a hydrophilic element for measurement or recordation purposes. The method includes depositing the silicate glass insulator onto the semiconductor wafer followed by the deposition of a moisture barrier, test transparent material onto the silicate glass insulator in a non-moisture containing environment. The semiconductor wafer can be placed in a moisture containing atmosphere. The measurement can be performed immediately or the semiconductor wafer can be stored and measurements taken later to accurately determine the concentration of the hydrophilic element in the silicate glass insulator.
The present invention further provides a method for processing a pilot or calibration silicon wafer having a BPTEOS or BPSG silicate glass insulator containing hydrophilic elements, such as boron and phosphorus, for measurement or recordation purposes. The method includes depositing the silicate glass insulator onto the silicon wafer followed by the deposition of a moisture barrier, test transparent material, such as an ultra-violet transparent nitride, onto the silicate glass insulator in a nitrogen containing environment. The semiconductor wafer can be placed in air. The measurement can be performed immediately or the semiconductor wafer can be stored without special precautions and measurements taken later to accurately determine the concentration of the boron and phosphorus in the silicate glass insulator.